An introduction to the philosophy of perception

Perception seen philosophically

• We perceive objects.– Conceived metaphysically:• What are the immediate objects of perception in

themselves? • What is there when you perceive an object?

– Conceived epistemologically:• How do we gain knowledge of what is outside our

minds?

The Syllabus: Direct realism

• the immediate objects of perception are mind-independent objects and their properties. – Issues, including:• the argument from illusion• the argument from perceptual variation (Russell’s

table example) • the argument from hallucination (the possibility of

experiences that are subjectively indistinguishable from veridical perception) • the time-lag argument.

The Syllabus: Indirect Realism

• the immediate objects of perception are mind-dependent objects that are caused by and represent mind- independent objects.

• Issues, including:– it leads to scepticism about the ‘existence’ of the external world (attacking

‘realism’) – responses to this (external world is the ‘best hypothesis’ (Russell); coherence of the various senses and lack of choice over our experiences (Locke))

– it leads to scepticism about the ‘nature’ of the external world (attacking ‘representative’) - responses (sense data tell us of ‘relations’ between objects (Russell); the distinction between primary and secondary qualities (Locke))

– problems arising from the view that mind-dependent objects represent mind-independent objects and are caused by mind-independent objects.

The Syllabus: Berkeley’s Idealism• the immediate objects of perception (i.e. ordinary objects

such as tables, chairs, etc) are mind-dependent objects. • Berkeley’s attack on the primary/secondary property

distinction and his ‘master’ argument. • Issues, including:

– it leads to solipsism– it does not give an adequate account of illusions and

hallucinations– it cannot secure objective space and time – whether God can be used to play the role He does.

Realism and Idealism in perception

• Perceptual realists, of whatever flavour, are committed to the following:– There are physical objects which are mind-

independent.– These physical objects are

• enduring • public

• Perceptual idealists, of whatever flavour, argue:– that physical objects are mind-dependent.– Physical objects are mental things in some way.

Theories of Perception, outlined

• Naïve or Direct Realism– Physical objects exist and their qualities are perceived

directly by the perceiver.

• Indirect Realism– Physical objects exist and their underlying physical

qualities generate perceptions in the mind of the perceiver.

• Idealism– Physical objects are simply perceptions in the mind of the

perceiver.

Direct or Naïve Realism

• Direct Realists: Thomas Reid• Direct realism:

– the immediate objects of perception are mind-independent objects and their properties

– which are perceived directly by the perceiver – so there are no intermediaries between object and perceiver– Question: ‘What do I perceive?’ ‘I directly perceive mind-

independent physical objects and their properties’.

Thomas Reid: Roses‘What is smell in the rose? It is a quality or virtue of the rose, or of something given off by the rose, which we perceive through the sense of smelling… What is smelling? It is an act of the mind, but is never imagined to be a quality of the mind. Again, the sensation of smelling is conceived to imply necessarily a mind or sentient being; but smell in the rose implies no such thing...So smell in the rose and the sensation that it causes are not thought of, even by the vulgar, as things of the same kind, although they have the same name.From what I have said we can learn that `the smell of a rose' signifies two things:• A sensation, which can't exist except when it is perceived, and can exist only in a

sentient being or mind.• Some power, quality or virtue in the rose, or in effluvia that it gives off, which has a

permanent existence independently of the mind and which by the constitution of nature produces the sensation in us.

We are fundamentally so built that we are led to believe that there is a permanent cause of the sensation, and are prompted to look for it; and experience leads us to locate it in the rose.

Direct Realism in Standard Form(nicked from University of Reading Philosophy dept.)

John Hospers, in ‘Philosophical Analysis’. He also suggests that these beliefs are shared “by virtually all human beings”.

1. There exists a world of material objects. 2. Statements about these objects can be known to be true through sense-

experience. 3. These objects exist not only when they are being perceived but also when they

are not perceived: the objects of perception are largely perception-independent. 4. These objects are also able to retain properties of the types we perceive them as

having even when they are not being perceived. Their properties are perception-independent.

5. By means of our senses, we perceive the world directly, and pretty much as it is. 6. So in the main, our claims to have knowledge of it are justified.

Four issues with Direct Realism

1. the argument from perceptual variation (Russell’s table example)

2. the argument from illusion (given, for example, by A.J. Ayer)

3. the argument from hallucination (the possibility of experiences that are subjectively indistinguishable from veridical perception)

4. the time-lag argument (Russell again).

The argument from perceptual variation: Russell’s table example

• To make our difficulties plain, let us concentrate attention on the table…as soon as we try to be more precise our troubles begin. Although I believe that the table is 'really' of the same colour all over, the parts that reflect the light look much brighter than the other parts, and some parts look white because of reflected light. I know that, if I move, the parts that reflect the light will be different, so that the apparent distribution of colours on the table will change…if several people are looking at the table at the same moment, no two of them will see exactly the same distribution of colours…It is evident from what we have found, that there is no colour which pre-eminently appears to be the colour of the table, or even of any one particular part of the table--it appears to be of different colours from different points of view, and there is no reason for regarding some of these as more really its colour than others…to avoid favouritism, we are compelled to deny that, in itself, the table has anyone particular colour.

• Russell then applies the same argument to the other senses which we might use to perceive the table.

Further developments of the perceptual variation argument

Further developments of the perceptual variation argument

The Perceptual Variation Argument in Standard Form

1. Perceptions of the same object vary.2. These variations occur without changes in the object

itself.3. So the properties physical objects really have and

those they appear to have are different.4. So what we are directly aware of in perception is not

exactly the same as what exists independently of our minds.

5. Therefore we do not perceive physical objects directly.

So, Mr Russell, what are we directly aware of in perception?

• ‘Let us give the name of 'sense-data' to the things that are immediately known in sensation: such things as colours, sounds, smells, hardnesses, roughnesses, and so on. We shall give the name 'sensation' to the experience of being immediately aware of these things. Thus, whenever we see a colour, we have a sensation of the colour, but the colour itself is a sense-datum, not a sensation. The colour is that of which we are immediately aware, and the awareness itself is the sensation. It is plain that if we are to know anything about the table, it must be by means of the sense-data--brown colour, oblong shape, smoothness, etc. – which we associate with the table; but, for the reasons which have been given, we cannot say that the table is the sense-data, or even that the sense-data are directly properties of the table. Thus a problem arises as to the relation of the sense-data to the real table, supposing there is such a thing.’ (Russell, ‘Problems of Philosophy’, Chapter 1)

• In other words, Russell uses the perceptual variation problem as an argument for indirect realism, by (re-)introducing the notion of sense-data which 1) are caused by physical objects; 2) and which cause our sensations in turn.

Responses the direct realist might make: relational properties

• This objection assumes that if something appears E to subject S, then S can only be immediately aware of something that in fact is E. – e.g. if a circular table looks elliptical from one angle, then it must be elliptical in itself.

• But the direct realist does not have to hold this view. (Bertrand Russell is setting up a straw man argument).

• Instead the direct realist can hold that external physical objects or events may appear other than they are, using the notion of relational properties i.e. a property an object has in relation to being perceived.– e.g. ‘to the left of’ is a relational property that depends on the relation between a

perceiver and an object.– ‘to the left of’ is a real property relating real objects. But it does vary between

perceivers.• So a circular object may have the relational property of ‘appearing elliptical’ to us

from a certain angle of view – which is not at all the same property as ‘being elliptical’.– e.g. it could look elliptical but be circular.

The Direct Realist’s Response, continued

• And direct realists can account for such properties by straightforwardly appealing to various physical and physiological considerations: – e.g. a circular table may look elliptical (or of another size) from a certain angle because of

perspectival distortion; – e.g. a copper penny of a certain hue may look to be of a different hue from another angle for

many reasons (lighting effects, the visual acuity of the viewer etc)• There is nothing in such commonplace facts which means we must posit the

existence of something other than physical objects as the objects of immediate awareness.

• And the notion of an ‘ideal observer’ seeing an object under normal lighting conditions whilst in a normal frame of mind etc and so knowing the real properties of the object is a perfectly defensible idea: this is what we mean when we say e.g. ‘the table is circular, and blue’ etc

• That is: we perceive physical objects, not sense-data, but not all properties of physical objects are mind-independent. (But! Is this the primary/secondary quality distinction here?)

Appearance and Reality: the arguments from illusion and hallucination

• These arguments should sound somewhat familiar. – What are they?– What’s the difference

between an illusion and a hallucination?

Ayer’s argument from illusion1. We perceive something having some property F e.g. a straight stick half

submerged in water which hence looks bent.2. When we perceive something having some property F then there is something

that has this property.3. But in the case of a perceptual illusion then the property F is not really

possessed by the object e.g. the stick is not really bent.4. So the property F must be a mental construct (a sense-datum or idea). (We only

know the stick is really straight by inference from previous data.)5. In perceptual illusions, we perceive sense-data and not physical objects directly.6. But illusions can be subjectively indistinguishable from veridical (=truthful)

perceptions.7. So in the case of both illusions and veridical perception we actually perceive

only sense-data. 8. So direct realism is false.

Countering the argument from illusion

• The argument involves a question-begging assumption that if something appears F to subject S, then S is immediately aware of something that is F.

• But Direct Realists can hold that object O may appear F to S, even though O is not F. – As with the argument from perceptual variation, the object may have relational

properties as well as directly perceived physical ones.– e.g. the stick may have the property of ‘looking bent when partly immersed in

water’ – and ‘looking bent’ and ‘being bent’ are different properties.• In addition, there are perfectly good scientific explanations of illusions

which don’t involve positing other objects of awareness beyond the directly physical– e.g. a straight stick submerged in water may look bent as water has a different

refractive index to air and so bends light differently. The straight stick's appearing bent is thus explainable without needing to posit some tertium quid which is bent.

the argument from hallucination

• What are hallucinations?– ‘prolonged experiences that are subjectively

indistinguishable from veridical perception’– Or: ‘perceptual illusions extended to cases where we think

we perceive things which in fact aren’t there at all (rather than just misperceiving the properties of things which are there to be perceived)’

– This kind of perceptual delusion is a more radical kind of perceptual error than simple illusion.

• Again, why would they be a problem for the direct realist?

The argument from hallucination in standard form

1. Consider the proverbial hallucinator. He is clearly immediately aware of something. For example, James Steward’s drunkard in the 1950 movie ‘Harvey’ consistently hallucinates interactions with a 6’ 8” rabbit.

2. But the object hallucinated does not actually exist. There is no Harvey the rabbit.

3. So the hallucinator can only be immediately aware of something other than an external physical object.

4. But there is no significant qualitative or phenomenal difference between the objects of awareness in cases of hallucination and in cases of veridical perception. Harvey and an actual six foot tall rabbit may be phenomenally indistinguishable to James Steward.

5. So we have reason to suppose that, since the objects of immediate awareness in hallucination are not external physical objects, the objects of immediate awareness in veridical perception are also not external physical objects.

6. So Direct Realism is false and the objects of direct awareness must be sense data and the like.

Countering the Argument from Hallucination

• The Argument from Hallucination may very well be the most powerful argument against Direct Realism, but it fails to refute it.

• Firstly even if we suppose for the sake of argument that sense-data (or ideas or the like) are the objects of immediate awareness in cases of hallucination, we need not accept that they are also the objects of immediate awareness in (veridical) perception. The proponent of the argument from hallucination assumes that if x and y are phenomenally indistinguishable, x and y are ontologically indistinguishable. If it walks like a duck, quacks like a duck, then it’s a duck.

• But counter-examples to this principle abound. A papier-mache barn might appear phenomenally indistinguishable from a real one; a fake Rolex might be physically incredibly similar to a real one.

• Second, let's allow James Stewart his direct awareness of Harvey. Even if a) Harvey doesn’t exist; and b) yet James Stewart is aware of something, we don’t have to conclude c) that he must be experiencing only sense-data or the like.

• There could be other perfectly good and perfectly scientific explanations of Harvey the rabbit. For instance:– In the special case of hallucinations, brain-states are the objects of

immediate awareness OR– In the special case of hallucinations, the objects of awareness are

mental images.

Countering the Argument from Hallucination

the time-lag argumentgiven by Russell in ‘The Problems of Philosophy’

1. We cannot perceive physical objects or events unless light is reflected or emitted by them and reaches our visual system.

2. Light travels at a finite velocity, and so there is always some time interval between the reflection or emission of light from a physical object or event and the light's reaching our eyes. Usually this interval is infinitesimal, because objects are usually close to us. But in the case of a distant star, or our sun, the time interval may be so considerable that, by the time the light reaches our eyes, the star may no longer exist.

3. If something no longer exists, we cannot now perceive it, let alone directly perceive it. And so, assuming the distant star no longer exists, we cannot directly perceive it when its light reaches our eyes. But since we are perceiving something, the object of (direct) perception must be something other than the distant star.

4. Though time lags are most significant in cases of distant objects such as stars, any time lag, however minute, between physical objects or events and our perception of them is incompatible with Direct Realism, for given the time lag, we cannot directly perceive physical objects and events as they presently are at the time of our perception. Since we perceive something, the object of (direct) perception must be something other than physical objects or events.

5. Direct Realism is false. We do not directly perceive physical objects and events. Enter sense-data, ideas etc.

Polaris, the North Star. It lies along Earth’s axis of rotation so

appears not to move in the night sky. It is 234 light-years or 234

trillion kilometres away. Is it still there now?

Countering the time-lag argument• Direct Realists can acknowledge the modern science of

perception:• in the vast majority of cases of perception of nearby physical objects

or events, perception occurs so quickly that it seems to occur instantaneously.

• But all perception involves a time lag, however short; • Astronomical perception simply has a more visible time lag because of

the distances involved. • So awareness of a celestial body which no longer exists is not odd. It’s

science.• Hence Direct Realists can concede the first two premises, and

need only focus on the third and fourth premises, the crux of the argument.

Countering the time-lag argument1. A confusion in the time-lag argument arises because the claim in

premise 3 ("if something no longer exists, we cannot now perceive it“) can be interpreted in at least two distinct ways:

1. if something no longer exists, we cannot now perceive it as it presently is. True. 2. if something no longer exists, we cannot now perceive it as it used to be.

Questionable. Surely we can now be aware of something as it was?

2. Scientific Direct Realists don’t make the claim that we can be aware of the no-longer existent object as it is now, but only that we can be aware of the once-existent object as it used to be.

3. So: from the physical fact that there are time lags in perception 1. It does not follow that we cannot directly perceive external physical objects or events.2. It only follows that we cannot directly perceive physical objects without a time lag. 3. But no scientific direct realist suggests human perception takes place instantaneously

(of course, we may feel that perception is instantaneous).

4. So direct realism is not defeated by the time-lag argument.